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memory leak in __build_skb (4)

Status: upstream: reported C repro on 2026/01/12 20:02
Subsystems: net
[Documentation on labels]
Reported-by: syzbot+4d8c7d16b0e95c0d0f0d@syzkaller.appspotmail.com
First crash: 6d09h, last: 6d09h
▶ ▼ Discussions (3)
Title Replies (including bot) Last reply
[PATCH v2 net 1/3] gue: Fix skb memleak with inner IP protocol 0. 1 (1) 2026/01/15 17:24
[PATCH v1 net 1/2] gue: Fix skb memleak with inner IP protocol 0. 2 (2) 2026/01/12 20:27
[syzbot] [net?] memory leak in __build_skb (4) 0 (1) 2026/01/12 20:02
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream memory leak in __build_skb (3) wireless 3 C 2 1112d 1110d 22/29 fixed on 2023/06/08 14:41
upstream memory leak in __build_skb (2) net 3 C 330 1333d 2323d 0/29 closed as invalid on 2022/10/12 18:48
upstream memory leak in __build_skb net 3 C 19 2401d 2431d 0/29 closed as invalid on 2019/08/12 12:07
▶ ▼ Last patch testing requests (1)
Created Duration User Patch Repo Result
2026/01/12 18:22 14m kuniyu@google.com patch upstream error

Sample crash report:
BUG: memory leak
unreferenced object 0xffff888109695a00 (size 240):
  comm "syz.0.17", pid 6088, jiffies 4294943096
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 40 c2 10 81 88 ff ff 00 00 00 00 00 00 00 00  .@..............
  backtrace (crc a84b336f):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4958 [inline]
    slab_alloc_node mm/slub.c:5263 [inline]
    kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270
    __build_skb+0x23/0x60 net/core/skbuff.c:474
    build_skb+0x20/0x190 net/core/skbuff.c:490
    __tun_build_skb drivers/net/tun.c:1541 [inline]
    tun_build_skb+0x4a1/0xa40 drivers/net/tun.c:1636
    tun_get_user+0xc12/0x2030 drivers/net/tun.c:1770
    tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999
    new_sync_write fs/read_write.c:593 [inline]
    vfs_write+0x45d/0x710 fs/read_write.c:686
    ksys_write+0xa7/0x170 fs/read_write.c:738
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff8881037b5e40 (size 192):
  comm "syz.0.17", pid 6088, jiffies 4294943096
  hex dump (first 32 bytes):
    00 40 9c 26 81 88 ff ff c0 66 0b 87 ff ff ff ff  .@.&.....f......
    21 52 bc 85 ff ff ff ff 00 00 00 00 00 00 00 00  !R..............
  backtrace (crc fcd1b1c6):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4958 [inline]
    slab_alloc_node mm/slub.c:5263 [inline]
    kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270
    dst_alloc+0x5b/0xe0 net/core/dst.c:89
    rt_dst_alloc+0x32/0xe0 net/ipv4/route.c:1651
    ip_route_input_slow+0xaa0/0x1560 net/ipv4/route.c:2429
    ip_route_input_rcu net/ipv4/route.c:2543 [inline]
    ip_route_input_noref+0xd1/0xe0 net/ipv4/route.c:2554
    ip_rcv_finish_core+0xca/0x7f0 net/ipv4/ip_input.c:368
    ip_rcv_finish net/ipv4/ip_input.c:451 [inline]
    NF_HOOK include/linux/netfilter.h:318 [inline]
    NF_HOOK include/linux/netfilter.h:312 [inline]
    ip_rcv+0x197/0x240 net/ipv4/ip_input.c:573
    __netif_receive_skb_one_core+0xd0/0x100 net/core/dev.c:6139
    __netif_receive_skb+0x1d/0x80 net/core/dev.c:6252
    netif_receive_skb_internal net/core/dev.c:6338 [inline]
    netif_receive_skb+0x49/0x240 net/core/dev.c:6397
    tun_rx_batched drivers/net/tun.c:1485 [inline]
    tun_get_user+0x1dbf/0x2030 drivers/net/tun.c:1953
    tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999
    new_sync_write fs/read_write.c:593 [inline]
    vfs_write+0x45d/0x710 fs/read_write.c:686
    ksys_write+0xa7/0x170 fs/read_write.c:738
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff8881095d2200 (size 240):
  comm "syz.0.18", pid 6092, jiffies 4294943097
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 40 c2 10 81 88 ff ff 00 00 00 00 00 00 00 00  .@..............
  backtrace (crc e1df1ba8):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4958 [inline]
    slab_alloc_node mm/slub.c:5263 [inline]
    kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270
    __build_skb+0x23/0x60 net/core/skbuff.c:474
    build_skb+0x20/0x190 net/core/skbuff.c:490
    __tun_build_skb drivers/net/tun.c:1541 [inline]
    tun_build_skb+0x4a1/0xa40 drivers/net/tun.c:1636
    tun_get_user+0xc12/0x2030 drivers/net/tun.c:1770
    tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999
    new_sync_write fs/read_write.c:593 [inline]
    vfs_write+0x45d/0x710 fs/read_write.c:686
    ksys_write+0xa7/0x170 fs/read_write.c:738
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff888109688800 (size 240):
  comm "syz.0.19", pid 6094, jiffies 4294943098
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 40 c2 10 81 88 ff ff 00 00 00 00 00 00 00 00  .@..............
  backtrace (crc 4b7eec9d):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4958 [inline]
    slab_alloc_node mm/slub.c:5263 [inline]
    kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270
    __build_skb+0x23/0x60 net/core/skbuff.c:474
    build_skb+0x20/0x190 net/core/skbuff.c:490
    __tun_build_skb drivers/net/tun.c:1541 [inline]
    tun_build_skb+0x4a1/0xa40 drivers/net/tun.c:1636
    tun_get_user+0xc12/0x2030 drivers/net/tun.c:1770
    tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999
    new_sync_write fs/read_write.c:593 [inline]
    vfs_write+0x45d/0x710 fs/read_write.c:686
    ksys_write+0xa7/0x170 fs/read_write.c:738
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

connection error: failed to recv *flatrpc.ExecutorMessageRawT: EOF

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/01/09 18:03 upstream 623fb9912f6a d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-gce-leak memory leak in __build_skb
* Struck through repros no longer work on HEAD.